This invention relates to the field of fruit and vegetable processing, and more particularly, this invention relates to controlling the discharge of pulp and juice in a juice finisher.
The juice extraction process is well known to those skilled in the art, such as described in U.S. Pat. No. 5,992,311, assigned to the present assignee, the disclosure which is hereby incorporated by reference in its entirety. A fruit, vegetable and the like is fed to a juice extractor, which acts as the primary extractor, and produces a pure liquid (juice) and a fibrous material (pulp) from fruit, vegetables and the like. After extraction, this mixture of juice and pulp is fed as a stream into a juice finisher, which is designed to separate the juice from the pulp.
The typical juice finisher used in a citrus processing facility includes either a screw type finisher and/or a paddle finisher. Both types of finishers rely on the juice to be extruded through a screen material, which regulates the size of the pulp that is maintained within the juice stream. Any pulp that is too large to be extruded through this screen is compressed by centrifugal and mechanical force, which is created by limiting the flow of pulp discharge either by a back pressure regulator and/or a weighted gate. With both types of finishers, the feed rate and the pulp-to-juice ratio of the feed material has a dramatic affect on the level of dryness at a given condition. Feed forward control is often used and based on historical data. It is usually used to control a screw type finisher. This type of control requires close monitoring as fruit conditions change.
The dryness of pulp can be determined within prior art systems by using the free liquid that is removed without the application of pressure, in a method known as the quick fiber method. This is the defacto standard for the calibration of finishers to maximize juice and juice by-products for yield and quality. Typically, a sample of pulp is brought to a laboratory where tests are conducted on the sample. For example, 200 grams of pulp sample are mixed with about 200 milliliters of water and stirred for a minute. This mixture sits for three minutes and is then stirred for another minute. The mixture is placed into a shaker with a 40 mesh screen for about three minutes and the liquid retrieved from the sample. The liquid is measured in a graduated cylinder where the amount of liquid measured (in milliliters) is called quick fiber. The total time is about 8-10 minutes, with even more time for preparation. This process is an established procedure that is time consuming. Additionally, the procedure has low accuracy, i.e., not repeatable, and high labor intensity, making this quick fiber method inefficient and costly.
Another drawback with prior art methods are the feed forward control. As noted before, the feed forward control is based on historical data, which is used to control a screw type finisher. This control requires close monitoring as fruit conditions change. Although feed forward control is better than simple manual control, it does not work on a paddle finisher and has no self-correction capability, thus eliminating the need for supervision.
U.S. Pat. No. 4,665,816 to Waters et al. discloses an apparatus that automatically controls a juice finishing machine. The temperature of juice solids in a pad area and temperature of initial juice entering the machine are separately monitored. A differential output signal is established and used for controlling machine operation. This is more complex than desired.
The present invention provides a system and method that advantageously controls the discharge of pulp and juice from a juice finisher without requiring the use of the more conventional quick fiber method. In accordance with one aspect of the present invention, a sample of pulp is obtained from juice, and pulp dryness measured using nuclear magnetic resonance (NMR). A juice and pulp processing system can be adjusted in response to the measured pulp dryness. In yet another aspect of the present invention, the discharge from the juice finisher that processes pulp and juice is measured using a nuclear magnetic resonance sensor. Based on the results of the NMR measurement, one of at least the juice injection into the juice finisher, the speed of the juice finisher, or the discharge pressure from the juice finisher is regulated.
In yet another aspect of the present invention, the NMR sensor measures the pulp dryness of pulp discharged from the juice finisher and compares the pulp dryness with a predetermined setpoint. If the pulp dryness differs from the predetermined setpoint, the speed of the juice finisher is changed. If the measured dryness is less than the predetermined setpoint, the speed of the finisher is decreased, and if the dryness is greater than the predetermined setpoint, the speed of the finisher is increased. The juice finisher could include a paddle type finisher.
In yet another aspect of the present invention, the NMR sensor measures the pulp dryness of pulp that is discharged from the juice finisher and compares the pulp dryness with a predetermined setpoint. If the pulp dryness differs from the predetermined setpoint, the pressure is changed within the juice finisher. In one aspect of the present invention, if the measured dryness is less than the predetermined setpoint, then the pressure is decreased. If the measured dryness is greater than the predetermined setpoint, the pressure is increased.
In yet another aspect of the present invention, the NMR sensor measures the ratio of pulp to juice in the juice finisher and compares the measured results with a predetermined setpoint. If the measured results differ from the setpoint, the juice injection into the finished pulp is changed for maintaining a desired pulp concentration level. If the measured results are less than the setpoint, the juice injection into the finished pulp is decreased. If the measured results are above the setpoint, the juice injection into the finished pulp is increased. The juice finisher could include a juice concentrator.
A fruit processing system also controls the discharge of pulp and juice and includes a juice finisher that receives juice and pulp from a juice extractor and separates the juice and pulp into a discharge substantially made of pulp and a discharge substantially made of juice. A nuclear magnetic resonance (NMR) sensor measures the dryness of the pulp discharged from the juice finisher. A controller compares the measured result with a predetermined setpoint and outputs a finisher control signal to the juice finisher for changing operation of the finisher.
In yet another aspect of the present invention, a variable speed drive is operatively connected to the juice finisher and responsive to the finisher control signal for decreasing the speed of the juice finisher if the measured dryness is less than a predetermined setpoint. The speed of the juice finisher is increased if the measured dryness is greater than the predetermined setpoint. A current-to-pressure transmitter can be connected to the juice finisher and responsive to a finisher control signal for decreasing pressure when the measured dryness is less than the predetermined setpoint and increasing pressure when the measured dryness is greater than the predetermined setpoint.
In yet another aspect of the present invention, the juice finisher is formed as a juice concentrator, i.e., pulp concentrator that separates juice and a juice and pulp mixture. The controller determines the ratio of pulp to juice in the juice and pulp mixture. A mixer receives the juice and pulp mixture. A portion of the juice is fed back from the juice finisher. A valve is operatively connected to the controller and operative for changing the flow of juice into the mixer.